Zinc smelting



w. A. oecs 1,988,608 ZINC SMELTING Patent ed Jan. '22, 1935 UNITED STATES PATENT, OFFICE zmc SMEL'IING William A. 08!, Cincinnati, Ohio Application April 18, 1934, Serial No. 121,184

GClaims. (ems-2s) This invention relates to the smelting of zinc and the object is to provide an improved process for recovering zinc from crude -"zinc-bearingmaterial such as roasted ore.

In my United States Patent 1,925,458 I have described a process of smelting zinc characterized by the treatment of the material in a thin layer by means of radiant heat incident on this layer and have indicated some of the advantages thereof as contrasted with the usual process of smelting by means of Belgian retorts. The present process obtains the advantages of that process with desirable features peculiar to itself.

My invention will be well understood by reference to the following description taken in connection with the accompanying drawings wherein I have shown in a general way a furnace adapted for the practice of the process and wherein-:-

Fig. 1 is a fragmentary longitudinal section of the furnace;

Fig. 2 is a fragmentary plan section on the line 22 of Fig. 1; and

Fig. 3 is a fragmentary view similar' to Fig. 1 but on a larger scale.

The process of my invention is exemplified by the operation of the equipment shown in the drawings and will be most easily understood by a preliminary description of that equipment. In these drawings there is partially shown an indirectly heated furnace which comprises a series of longitudinally adjacent, long and narrow reaction chambers 9, Fig. 2 indicating the fact that a number of such chambers are provided. These chambers have roofs 11, preferably of the construction hereinafter more specifically described, formed of heat-resisting material of high heatconducting capacity. At one end of the chamber is provided a vapor ofitake 13 which may lead to a condenser or the like and at the otherend is a charging opening 15. Above the roofs 11 is a combustion chamber 17 defined by the overlying roof 19 of the furnace as a whole. In this combustion chamber fuel is burned to highly heat the roofs 11 transmitting heat therethrough to be radiated from the inner surfaces thereof to the underlying charge material in the reaction chambers. For, this' purpose there may be embodied in the furnace a suitable regenerating system unnecessary hereto illustrate. To insure effective heating of the charge the roofs 11 of the combustion chambers must be thin and they also must be adapted to withstand the high heat produced in the combustion chamber. I preferably form them of tiles of suitable heat-resisting material consisting essentially of silicon carbide.

A material of this nature is well known commercially under the trade name Carbofrax. While the heat is applied to the charge by radiation from the inner surface of the roof, the trans-,

fer of heat to that radiating surface is, of course,

by conduction through the material of the roof which is dependent upon the area of the roof and its thickness. To provide for adequate heat transfer while providing a large margin of safety for structural strength and wearing qualities 0 in the rciof 11, I preferably so construct it that with a substantially uniform thickness its surface area is markedly in excess of its projected area, the roof thus having a generally corrugated form. Herein the roof is formed of tiles 11 which 15 might be described as of basin-like form or otherwise as in the form of a hollow frustum of a pyramid. Preferably their length is such as to bridge across from one sidewall of a reaction chamber to another. This arrangement not only 20 provides for a greatly increased transfer of heat as compared with a fiat roof, whereby for a given thickness of tile adequately high temperatures can more readily be attained at the radiating surface, but the shape disclosed obviously provides substantial structural strength in the tile itself permitting a relatively thin wall to be used with safety.

As the reaction chambers are generally similar, i will be suflicient in the following description to speak of one alone. What corresponds to the sole of the chamber in the ordinary furnace is herein formed as a shallow container 21 adapted to contain a bath of material of high specific gravity and high boiling point which will be liq- 3 uid at the reaction temperatures involved. For this purpose I prefer to utilize iron as indicated bythe notation of the chemical symbol Fe in themanner of a reference numeral upon the bath in the container. An end wall 23, herein that ad- 4 jacent the vapor offtake 13 of this containen is made slightly lower than the adjacent walls, thus forming a weir, the bath of iron brimming to the edge of the weir. Any material such as molten slag which floats on the surface of the bath may 4 thus be discharged over the weir 23 to the slag channel 25 from which it may be tapped as desired through tap openings 27.

In alignment with the charging opening 15 I show a gas-tight antechamber 29. The inner end of the roof of this chamber has an opening therein to receive the outlet of a charge hopper 31 having the rotatable vaned measuring'wheel 33 therein. As the space between two of the vanes of the measuring wheel is presented to the outlet of the hopper, the measured quantity of material received between these vanes is deposited on the floor of the antechamber adjacent the charging opening 15. This quantity of charge is advanced onto the surface of the metal bath in container 21 by means of a plunger 35 carried by rods 37 formed as racks to cooperate (see Fig. 3) with pinions 39 suitably driven from a reversible electric motor 41. This plunger is made of chrome iron to permit its use under the high temperature conditions involved and, as best seen in Fig. 3, has a back, top and side walls but no bottom or front end. As the plunger moves forward it confines the measured amount ofcharge material delivered from the hopper and moves it forward as a mass of substantially the width of the bath until it is deposited from the open bottom of the plunger upon the surface of the bath.

I have now described in a general way the salient features of the mechanism illustrated by means of which my process may be practised. The crude charge material consists, for example, of roasted zinc ore,and reduction material, the latter being present preferably only substantially in the theoretical amount required to effect the reaction. The rationale of my process is to distribute this material as a thin layer over the surface of the bath to fioat freely thereon substantially under the influence of gravity alone and while so exposed to effect the reaction by radiant heat supplied to the surface of the layer through the roof 11 of the reaction chamber. By thin I mean a thickness, which in practice may be about /z inch or less, such that the residue accumulated during the complete utilization of the material during the process will not substantially impair the transfer of heat as manifested by a substantial decrease in the rate of vapor evolution. In other words, the efliciency of extraction remains substantially constant during what is, commercially speaking, a substantially complete removal of the metal values without any loss in efficiency due to the accumulation of residues which would blanket the remaining unreduced crude material and cause a'marked decrease in the thermal efliciency of the process. My purposes exclude the promiscuous dumping of a substantial column of the material into the furnace which could be distributed, if at all, only at the cost of objectionable mechanical disturbance. The body of material carried by the feeding plunger 35 at a single stroke will be of a volume much less than would provide a layer of desired thickness over the entire surface of the bath, that is, a complete charge is fed only by a number of strokes of the plunger. The reaction, of course, proceeds continuously. The increment of charge carried by the plunger may be of a width substantially equal to that of the bath, but may also be substantially thicker than the desired layer as I have found that such a volume will distribute itself over the surface of the molten iron; The intermittent action of the reciprocating feed device facilitates this distributing action while nevertheless a substantial continuous supply of material to the furnace may be maintained. Each increment of charge also gently pushes forward the floating material from the previous charges. It is unnecessary to limit the amount of heat to avoid slagging of the residues, such slagging being desirable rather than otherwise, as the molten slag will float on the surface of the bath and may overflow at the weir 23. It appears that there is provided a gentle surface curfent of the floating material over the surface or the quiescent bath which promotes the distribution of the charge thereover. As direct observation of the action is, of course, diflicult, these statements are to a certain degree conjectural and the relative influence of the various probable factors here suggested cannot be estimated. However, the general effect is that the material without violent agitation or tumbling floats freely on the surface of the bath substantially under the influence of gravity alone and is gently wafted along the surface in a manner sharply contrasted with the dragging or forcible feed of similar powdery material over a solid supporting surface. The feeding of a substantial volume of material is quickly and efliciently performed by mechanical means, yet a sufficiently thin'layer is provided to permit the metal values to'be completely and efficiently disengaged without building up an insulating resistance by accumulation of residues.

Thevapors resultant from the reduction pass through the oiftakes 13 and go to a condenser or may be otherwise disposed of.

The furnace herein disclosed resembles in some respects that of my application Serial No. 710,783, filed Feb. 12, 1934, and claims in that application cover certain features herein disclosed. Without limitation to specific dimensions, I may saythat suitable dimensions for the bath might be ten feet long and three feet wide, a suitable number of reaction chambers being ganged together to permit eflicient heating. The increment of charge carried by the plunger may be about an inch or more in thickness and three or four inches in fore and aft depth.

By the use of such a furnace as that shown suitably high temperatures are economically attained which permit the use of iron as a preferred material for the bath. Any iron which is vaporized may be separated from the condensed zinc by eliquation if necessary. However, the amount of iron will be small on account of its high boiling point so that only a minute quantity of the bath will be vaporized. In this connection it may be recalled that ordinary prime western spelter" may contain up to .08% iron. Other material,

however, may be utilized for the bath. For example, if a substantial amount of lead in the product is unobjectionable or desired, lead may be used. In that case, however, a substantial amount of lead will vaporize and the bath must be kept replenished.

I am aware that the invention may be embodied in other specific forms without departing from the spirit or essential attributes thereof, and I therefore desire the present embodiment to be considered in all respects as illustrative and not restrictive; reference being had to the appended claims rather than to the foregoing description to indicate the scope of the invention.

I claim:

1. The method of recovering zinc from an uncompacted mixture of crude oxide and carboniferous material characterized by the features that a layer of material of greater weight and of lesser volatility than zinc and which is liquid at the temperatures involved is maintained in an indirectly heated furnace to provide a bath therein and that the mixture is supplied to the surface of the bath to float thereon as an extended layer subduring the process will not substantially impair the transfer of heat, as manifested by a substantial decrease in the rate of vapor evolution.

2. The method of recovering zinc from an uncompacted mixture of crude oxide and carboniferous material characterized by the features that a layer of material of greater weight and of lesser volatility than zinc and which is liquid at the temperatures involved is maintained in an indirectly heated furnace to provide a bath therein and that the mixture is supplied to the surface of the bath at one end thereof to float thereon as an extended layer substantially under the influence of gravity alone, that heat is supplied thereto substantially uniformly over the surface of the bath substantially by radiation alone, and that nongaseous supernatant residues are withdrawn at the opposite end of the bathto provide a surface current of material along the bath, the layer being of such maximum thickness that the residue accumulated during the complete utilization of the material during the process will not substantially impair the transfer of heat, as manifested by a substantial decrease in the rate of vapor evolution. 1

3. The method of recovering zinc from anuncompacted mixture of crude oxide and carboniferous material characterized by the features that the mixture is supplied to the surface of a bath of molten iron in an indirectly heated furnace to float thereon as an extended layer substantially under the influence of gravity alone and that heat is supplied thereto substantially uniformly over the surface of the bath substantially by radiation alone, the layer being of such maximum thickness that the residue accumulated during the complete utilization of the material during the process will not substantially impair the transfer of heat, as manifested by a substantial decrease in the rate of vapor evolution.

4. The method of recovering zinc from an uncompaoted mixture of crude oxide and carboniferous material characterized by the features that the mixture is supplied to the surface of a bath of molten iron in an indirectly heated furnace at one end thereof to float thereon as an extended layer substantially under the influence of gravity alone, that heat is supplied thereto substantially uniformly over the surface of the bath substantially by radiation alone, and that non-gaseous supernatant residues are withdrawn at the opposite end of the bath to provide a surface current of material along the bath, the layer being of such maximum thickness that the residue accumulated during the complete utilization of the mateheated furnace to provide a bath therein and that batches of the mixture are intermittently delivered at one end of the bath to the surface thereof to be distributed thereover as an extended layer floating thereon substantially under the influence of gravity alone and that heat is supplied thereto substantially uniformly over the surface of the bath substantially by radiation .alone, the layer being of such maximum'thickness that the residue accumulated during the complete utilization of the material during the process will not substantially impair the transfer of heat, as manifested by a substantial decrease in the rate of vapor evolution.

6. The method of recovering zinc from an uncompacted mixture of crude oxide and carboniferous material characterized by the features that a layer of 'material of greater weight and of lesser volatility than zinc and which is liquid at the temperatures involved is maintained in an indirectly heated furnace to provide a bath therein and that the material in the form of a thin floating layer is wafted along the surface of the bath and that heat is supplied thereto substantially uniformly over the surface of the bath substantially by radiation alone, the layer being of such maximum thickness that the residue accumulated during the complete utilization of the material during the process will not substantially impair the transfer of heat, 'as manifested by a substantial decrease in the rate of vapor evolution.

WILLIAM A. OGG. 

